Effects of proteinase inhibitor from Adenanthera pavonina seeds on short- and long term larval development of Aedes aegypti

Phytochemical prospection, hemagglutinating and insecticidal activity of saline extracts from the seeds of Tamboril (Enterolobium contortisiliquum) Vell. Morong (Fabaceae) on Aedes aegypti (Diptera: Culicidae)

This study evaluated the insecticidal activity of crude extracts from Enterolobium contortisiliquum (Vell.) seeds on eggs and larvae of A. aegypti, and also verified the phytochemical profile and the presence of lectins in the extract. The 0.15 M NaCl saline solution was used as the extracting substance. For tests with eggs and larvae, the crude extract was used in its raw form (RCE) and boiled at 100º C for 5 min (BCE). Concentrations of 4.68; 9.37; 18.75; 28.13; 37.13 and 46.89 mg/mL, with distilled water as a negative control. Assays were performed in triplicate. The results were subjected to analysis of variance, Tukey's test and Log-Probit analysis to determine LC50 and LC90. BCE showed better results on eggs than RCE, managing to prevent the hatching of larvae in 81.66% ± 10.40 of treated eggs, at a concentration of 46.89 mg/mL. The LC50 and LC90 were set at 35.95 and 52.67 mg/mL, respectively. In tests with larvae, concentrations of 46.89 and 37.13 mg/mL, for RCE and BCE, caused 100% mortality in 24 hours of exposure. Larval mortality at the other concentrations increased with exposure time extending to 48 h. RCE, at 48 h exposure is the most promising extract on larvae (E = 72.77%, LC90 = 10.86 mg/mL). In RCE, the presence of lectins and secondary metabolites: flavonoids, xanthones and phenols, were detected. The results demonstrate the potential of E. contortisiliquum seed extracts with ovicidal and larvicidal action on A. aegypti.

Tephrosia toxicaria (Sw.) Pers. extracts: Screening by examining aedicidal action under laboratory and field conditions along with its antioxidant, antileishmanial, and antimicrobial activities

An increase in the incidence of arboviral, microbial and parasitic infections, and to disorders related to oxidative stress has encouraged the development of adjuvant therapies based on natural formulations, such as those involving plant extracts. Thus, to expand the repertoire of the available therapeutic options, this study aimed to describe the versatility of Tephrosia toxicaria (Sw.) (Pers., 1807) extracts for the control of arbovirus vectors, as well as their antioxidant, antileishmanial, and antimicrobial potential. Among the aqueous and hydroethanolic extracts obtained, the hydroethanolic extract from roots (RHA) was identified as the most active larvicide extract demonstrating, respectively, the lowest lethal concentration (mg/mL) for 50%, 90% and 99% of Aedes aegypti (L., 1762) and Aedes albopictus (S., 1894) larvae, observed at 24 h (0.33, 0.84 and 1.80; 0.32, 0.70 and 1.32) and 48 h (0.17, 0.51 and 1.22; 0.26, 0.47 and 0.78) post-exposure. Field assays revealed that RHA (0.84 mg/mL) is a potential oviposition deterrent, reducing egg-laying by approximately 90%. RHA (0.1 mg/mL) also exhibited antioxidant activity for the following tests: total antioxidant capacity (286.86 mg AAE/g), iron (87.16%) and copper (25.64%) chelation, and superoxide scavenging (10%). In the cell culture assays, RHA (0.1 mg/mL) promoted regeneration of metabolic activity (92% cell viability) in cells exposed to oxidative stress. Furthermore, RHA displayed weak antileishmanial activity (IC50 = 3.53 mg/mL) against Leishmania amazonensis and not exhibit antimicrobial activity. The extraction favored the concentration of carbohydrates in RHA, in addition to lectins and protease inhibitors, with molecular masses estimated between 10 and 24 kDa. Cytotoxicity and phytotoxicity analyses of RHA suggested its biosecurity. Thus, RHA is a multivalent extract with insecticide and antioxidant properties at low and safe concentrations. However, others studies on its indirect toxic effects are ongoing to ensure the complete safety of RHA.

Isolation, Purification, and Characterization of Homogenous Novel Bioactive Protein from Datura stramonium Stem Exhibited Larvicidal Activity against Anopheles stephensi

The insecticidal resistance of mosquitoes necessitates the development of a natural, safe, and plant-based method for vector control. Unfortunately, there are no effective vaccines or particular medications available to combat malaria; therefore, mosquitoes must be targeted directly. Previous studies have shown the health benefits of Datura stramonium, but its bioactive peptides or proteins are less explored. This is the first study on D. stramonium stem protein used for mosquito larval protein. The present study aimed to identify the purified mosquito larval protein from the crude extract of D. stramonium stem. Crude protein was isolated, precipitated, dialyzed, and purified by using ion-exchange chromatography, native PAGE, and HPLC. The highest larval mortality was observed at 5.5 mg/ml of crude protein concentration. Native PAGE was used for the analysis and purification of active proteins. The single homogeneous purified larvicidal protein appeared as a single band of 30 kDa by SDS-PAGE. The novel bioactive peptide was characterized by LC-MS/ESI-MS. The homology of the peptide was searched by the Mascot search engine. The database search revealed has not shown peptide similarity with D. stramonium protein, but homology with another plant Arabidopsis thaliana protein is probable for protein phosphatases. The lethal concentration of purified protein against 3rd instar larvae of Anopheles stephensi had LC50 and LC90 values of 25 μg/ml and 40 μg/ml. It has shown new insight into larvicidal activity and can be used as a new drug against malaria and other mosquito-borne diseases.

Plant Kunitz Inhibitors and Their Interaction with Proteases: Current and Potential Pharmacological Targets

The action of proteases can be controlled by several mechanisms, including regulation through gene expression; post-translational modifications, such as glycosylation; zymogen activation; targeting specific compartments, such as lysosomes and mitochondria; and blocking proteolysis using endogenous inhibitors. Protease inhibitors are important molecules to be explored for the control of proteolytic processes in organisms because of their ability to act on several proteases. In this context, plants synthesize numerous proteins that contribute to protection against attacks by microorganisms (fungi and bacteria) and/or invertebrates (insects and nematodes) through the inhibition of proteases in these organisms. These proteins are widely distributed in the plant kingdom, and are present in higher concentrations in legume seeds (compared to other organs and other botanical families), motivating studies on their inhibitory effects in various organisms, including humans. In most cases, the biological roles of these proteins have been assigned based mostly on their in vitro action, as is the case with enzyme inhibitors. This review highlights the structural evolution, function, and wide variety of effects of plant Kunitz protease inhibitors, and their potential for pharmaceutical application based on their interactions with different proteases.

Adenanthera pavonina, a potential plant-based protein resource: Seed protein composition and immunohistochemical localization of trypsin inhibitors

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Trypsin inhibitors are abundant in the seeds of Adenanthera pavonina.

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A. pavonina trypsin inhibitors cross react with soybean trypsin inhibitor antibodies.

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Boiling A. pavonina seeds inactivates the trypsin inhibitors.

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A. pavonina trypsin inhibitors are resistant to pepsin digestion.

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A. pavonina trypsin inhibitors are localized in the cell cytosol.

Adenanthera pavonina, an underutilized tropical tree, is being promoted as an alternative food source for meeting the nutritional needs of human and animals. In this study, we have shown that trypsin inhibitors as one of the predominant proteins in the seeds of A. pavonina. DE-52 column chromatography resulted in the identification of four peaks with trypsin inhibitor activity. SDS-PAGE and immunoblot analyses revealed DE-52 peaks A and B were enriched in 17 and 15 kDa proteins and these proteins cross-reacted against soybean trypsin inhibitor antibodies. Simulated gastric fluid digestion revealed that the 15–17 kDa proteins are resistant to pepsin digestion. Roasting the seeds lowered the trypsin inhibitor activity while boiling intact seeds elevated the enzyme activity. However, the trypsin inhibitor activity was completely abolished when the seeds were boiled without their seed coats. Immunohistochemical detection and confocal microscopy demonstrated that trypsin inhibitors were localized in the cell cytosol.

Trypsin inhibitor from Enterolobium contortisiliquum seeds impairs Aedes aegypti development and enhances the activity of Bacillus thuringiensis toxins

BACKGROUND

Disease vector insects are barriers for human development. The use of synthetic chemicals to control these vectors has caused damage to the environment and contributed to the arising of resistant insect populations. This has led to an increased search for plant-derived molecules with insecticidal activity or that show synergistic effects with known insecticidal substances, such as protease inhibitors. Thus, we aimed to evaluate the effect of Enterolobium contortisiliquum trypsin inhibitor (EcTI) on Aedes aegypti development as well as its effect on insecticidal activity of Bacillus thuringiensis toxins.

RESULTS

EcTI showed an apparent molecular mass about of 20 kDa in SDS-PAGE and was able to inhibit in vitro the activity of trypsin and proteases from midgut of Ae. aegypti larvae. EcTI was not able to cause acute toxicity on mosquito larvae even at 1000 μg mL^-1 , however it promoted a delay in larval development after prolonged exposure. The zymogram results for EcTI-treated larvae (from 50 to 200 μg mL^-1 ) showed an increase of midgut proteases activity as a larvae defense mechanism, however no changes in the enzyme profile was observed. These same concentrations were able to enhance up to three fold the insecticidal activity of B. thuringiensis toxins without causing toxicity to Artemia sp. nauplii, a non-target organism.

CONCLUSIONS

The results offer a novel approach by combining EcTI and B. thuringiensis toxins for combating Ae. aegypti larvae. © 2020 Society of Chemical Industry.

Noncompetitive tight-binding inhibition of Anticarsia gemmatalis trypsins by Adenanthera pavonina protease inhibitor affects larvae survival

The economic loss in soybean crops caused by the Lepidoptera insects has encouraged the search for new strategies to control this pest, which are currently based on synthetic insecticides. This paper evaluated the ability of ApTI (Adenanthera pavonina trypsin inhibitor) to inhibit trypsin-like proteins from Anticarsia gemmatalis by docking, molecular dynamics, and enzymatic and survival assay. The docking and molecular dynamic simulation between trypsin and ApTI were performed using the program CLUSPRO and NAMD, respectively. The inhibitory constant K_i and the inhibition type were determined through chromogenic assays. The survival assay of neonatal larvae under treatment with artificial diet supplemented with ApTI was also performed. The ApTI binding site was predicted to block substrate access to trypsin due to four interactions with the enzyme, producing a complex with a surface area of 1,183.7 Ų . The kinetic analysis revealed a noncompetitive tight-binding mechanism. The survival curves obtained using Kaplan-Meier estimators indicated that the highest larvae mortality was 60%, using 1.2 mg of ApTI per 100 ml of artificial diet. The in vitro, in vivo, and in silico studies demonstrated that ApTI is a strong noncompetitive inhibitor of trypsin with biotechnological potential for the control of A. gemmatalis insect.

Dual Insecticidal Effects of Adenanthera pavonina Kunitz-Type Inhibitor on Plodia interpunctella is Mediated by Digestive Enzymes Inhibition and Chitin-Binding Properties

The Indianmeal moth, Plodia interpunctella, is one of the most damaging pests of stored products. We investigated the insecticidal properties of ApKTI, a Kunitz trypsin inhibitor from Adenanthera pavonina seeds, against P. interpunctella larvae through bioassays with artificial diet. ApKTI-fed larvae showed reduction of up to 88% on larval weight and 75% in survival. Trypsin enzymes extracted from P. interpunctella larvae were inhibited by ApKTI, which also demonstrated capacity to bind to chitin. Kinetic studies revealed a non-competitive inhibition mechanism of ApKTI for trypsin, which were further corroborated by molecular docking studies. Furthermore, we have demonstrated that ApKTI exhibits a hydrophobic pocket near the reactive site loop probably involved in chitin interactions. Taken together, these data suggested that the insecticidal activity of ApKTI for P. interpunctella larvae involves a dual and promiscuous mechanisms biding to two completely different targets. Both processes might impair the P. interpunctella larval digestive process, leading to larvae death before reaching the pupal stage. Further studies are encouraged using ApKTI as a biotechnological tool to control insect pests in field conditions.

Plant defenses interact with insect enteric bacteria by initiating a leaky gut syndrome

Plants produce suites of defenses that can collectively deter and reduce herbivory. Many defenses target the insect digestive system, with some altering the protective peritrophic matrix (PM) and causing increased permeability. The PM is responsible for multiple digestive functions, including reducing infections from potential pathogenic microbes. In our study, we developed axenic and gnotobiotic methods for fall armyworm (Spodoptera frugiperda) and tested how particular members present in the gut community influence interactions with plant defenses that can alter PM permeability. We observed interactions between gut bacteria with plant resistance. Axenic insects grew more but displayed lower immune-based responses compared with those possessing Enterococcus, Klebsiella, and Enterobacter isolates from field-collected larvae. While gut bacteria reduced performance of larvae fed on plants, none of the isolates produced mortality when injected directly into the hemocoel. Our results strongly suggest that plant physical and chemical defenses not only act directly upon the insect, but also have some interplay with the herbivore's microbiome. Combined direct and indirect, microbe-mediated assaults by maize defenses on the fall armyworm on the insect digestive and immune system reduced growth and elevated mortality in these insects. These results imply that plant-insect interactions should be considered in the context of potential mediation by the insect gut microbiome.

Insect midgut structures and molecules as targets of plant-derived protease inhibitors and lectins

The midgut of insects is involved in digestion, osmoregulation and immunity. Although several defensive strategies are present in this organ, its organization and function may be disturbed by some insecticidal agents, including bioactive proteins like lectins and protease inhibitors (PIs) from plants. PIs interfere with digestion, leading to poor nutrient absorption and decreasing amino acid bioavailability. Intake of PIs can delay development, cause deformities and reduce fertility. Ingestion of PIs may lead to changes in the set of proteases secreted in the insect gut, but this response is often insufficient and results in aggravation of the malnutrition status. Lectins are proteins that are able to interact with glycoconjugates, including those linked to cell surfaces. Their effects on the midgut include disruption of the peritrophic matrix, brush border and secretory cell layer; induction of apoptosis and oxidative stress; interference with nutrient absorption and transport proteins; and damaging effects on symbionts. In addition, lectins can cross the intestinal barrier and reach the hemolymph. The establishment of resistant insect populations due to selective pressure resulting from massive use of a bioactive protein is an actual possibility, but this can be minimized by the multiple mode-of-action of these proteins, mainly the lectins. © 2018 Society of Chemical Industry.

First insights into insecticidal activity against Aedes aegypti and partial biochemical characterization of a novel low molecular mass chymotrypsin-trypsin inhibitor purified from Lonchocarpus sericeus seeds

BACKGROUND

Arboviroses such as dengue, Zika and chikungunya represent a serious public health issue as a consequence of the absence of approved vaccines or specific antiviral drugs against the arboviruses that cause them. One way to prevent these diseases is by combating the vector mosquito, Aedes aegypti (Diptera), which has serine proteases in the midgut. Protease inhibitors are molecules that can block enzyme activity, impairing digestion and nutrition, which can lead to death. Thus, we purified and characterized a novel chymotrypsin-trypsin inhibitor (LsCTI) from Lonchocarpus sericeus seeds and investigated its effect upon Ae. aegypti egg hatching, larval development and digestive proteases.

RESULTS

LsCTI showed a single protein band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and the molecular mass determined by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was 8870.45 Da. Kinetics analyses revealed a noncompetitive type of inhibition and low inhibition constant (K_i ) for chymotrypsin (8.24 x 10^-8 m). The thermal resistance was remarkable, even at 100 °C for 180 min. The inhibitor concentration required for 50-percent enzyme inhibition (IC₅₀ ) of LsCTI was 4.7 x 10^-7 m for Ae. aegypti midgut larval enzymes. LsCTI did not affect egg hatchability at 0.3 mg mL^-1 , but caused a high larval mortality rate (77%) and delayed development (37%).

CONCLUSIONS

LsCTI is a novel protease inhibitor with remarkable biochemical characteristics and is a potential tool to control Ae. aegypti development. © 2017 Society of Chemical Industry.

Development of an eco-friendly mosquitocidal agent from Alangium salvifolium against the dengue vector Aedes aegypti and its biosafety on the aquatic predator

Plant extracts with their enriched chemical constituents have established potential alternative mosquito control agents. In this research, we developed an eco-friendly mosquitocidal agent from Alangium salvifolium leaves against the dengue and Zika virus vector Aedes aegypti and we investigated its biosafety on the mosquito aquatic predator Toxorhynchites splendens. Results showed that the methanolic extract of A. salvifolium leaves was composed by eight main compounds, with major peak area for hexadecenoic acid (21.74%). LC₅₀ and LC₉₀ values calculated on Ae. aegypti fourth instar larvae were 104.80 and 269.15 ppm respectively. The methanolic extract tested at 100 ppm decreased the α-β carboxylesterase and SOD ratio significantly and upregulated the GST and CYP450 level. The A. salvifolium methanolic extract displayed significant repellent and adulticidal activity at 100 and 400 ppm respectively. The treatment with 100 ppm of the methanolic extract led to 210 min of protection from Ae. aegypti bites. Four hundred parts per million of the extract showed 98% adult mortality within 30 min from the treatment. Lastly, biosafety assays on the mosquito aquatic predator Tx. splendens showed that the toxicity of the A. salvifolium extract was significantly lower if compared to the cypermethrin-based treatments. The methanolic extract of A. salvifolium showed a maximum of 47.3% mortality rate at the concentration of 1000 ppm, while 0.7 ppm of cypermethrin achieved 91.3% mortality rate on Tx. splendens. Overall, our study enhances basic knowledge on how to improve natural larvicidal agents against dengue and Zika virus mosquito vector with harmless responses on non-target aquatic predators.

Trypsin inhibitor from Leucaena leucocephala seeds delays and disrupts the development of Aedes aegypti, a multiple-disease vector

BACKGROUND

Nowadays, the Aedes aegypti mosquito represents a serious public health issue in view of the large outbreaks of the arboviral diseases zika, dengue, chikungunya and yellow fever. This holometabolous insect has midgut digestive enzymes that are trypsin- and chymotrypsin-like proteins. Protease inhibitors are able to bind to proteolytic enzymes and promote a blockage in digestion and nutrition, leading to death. Thus, we investigated the effect of trypsin inhibitor of Leucaena leucocephala (LTI) seeds on egg hatching, larval development and digestive midgut proteases.

RESULTS

LTI was obtained by trichloroacetic acid precipitation followed by a single chromatography step on anhydrous trypsin sepharose. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate showed a single protein band with a molecular mass close to 20 kDa. After exposure of Ae. aegypti eggs to LTI (0.3 mg mL^-1 ), egg hatching was reduced (50%). LTI did not show acute toxicity on newly hatched larvae incubated under the same conditions, but after 10 days of exposure a high mortality rate (86%) was observed and the surviving larvae had a 25% delay in development. LTI was able to inhibit in vitro the midgut enzymatic activity (70%), and when larvae were incubated with LTI solution we observed an inhibition of 56%.

CONCLUSIONS

LTI is a promising new tool to control critical points of Ae. aegypti development. © 2016 Society of Chemical Industry.